1. Field of the Invention
The present invention relates to gyros. More particularly, it relates to an optical gyro whose detection range for angular velocities is wide. Further, it relates to a semiconductor device which has a laser diode of a ring resonator type.
2. Related Background Art
Heretofore, a mechanical gyro having a rotor or a vibrator, and an optical gyro have been known as gyros each of which is used for detecting the angular velocity of a moving object. In particular, the optical gyro is capable of instantaneous start and has a wide dynamic range, and it is therefore innovating in the field of gyro technology. Such optical gyros include a laser gyro of ring resonator type, an optical fiber gyro, a gyro of passive ring resonator type, etc. Among them, a ring resonator type laser gyro employing a gas laser was begun to be developed earliest, and it has already been put to practical use for aircraft etc. Recently, a ring resonator type laser gyro of small size and high precision has also been proposed, and one disclosed in the official gazette of Japanese Patent Application Laid-open No. 5-288556 is mentioned as an example. With such an optical gyro, a semiconductor ring resonator type laser is formed on a single substrate, clockwise and counterclockwise lights outputted from a ring waveguide are detected by a single photodetector outside a ring resonator, and the beat signal of the lights is detected, thereby to detect an angular velocity.
FIG. 15 of the accompanying drawings is a top plan view of the ring resonator type laser gyro contained in the official gazette of Japanese Patent Application Laid-open No. 5-288556. Numeral 110 designates a semiconductor substrate, numeral 111 a gain waveguide, numeral 112 reflective surfaces, numerals 113 and 114 output surfaces, numerals 118 and 119 lights delivered from the respective output surfaces 113 and 114, numeral 117 a photodetector, and numerals 122 and 123 electrodes. In case of the gyro shown in FIG. 15, lasing lights are generated in the gain waveguide 111 having the reflective surfaces 112, by injecting a current. The wavelengths of the clockwise light 115 and the counterclockwise light 116 differ in accordance with an angular velocity, and the two output lights 118 and 119 (corresponding to the clockwise and counterclockwise lights 115 and 116, respectively) interfere on the photodetector 117. Thus, the angular velocity is outputted as a voltage change from the electrode 123.
With the prior-art example, however, the size of the laser gyro becomes large for the reason that a beat signal is detected by deriving the clockwise light and counterclockwise light which travel within the ring waveguide, and causing the lights to interfere on the photodetector. Further, a gyro of higher detection sensitivity or wider detection range for angular velocities has been requested.